1. Field of the Invention
The present invention relates to an image capture apparatus and, more particularly, to an image capture apparatus for capturing a moving image.
2. Description of the Related Art
As is conventionally known, when an image capture apparatus using a CCD or CMOS sensor captures a moving image under fluorescent light connected to the commercial power supply, the brightness may vary for each frame or light/dark horizontal stripes may be generated in a frame due to blinking of the fluorescent light at the frequency of the commercial power supply. This light/dark variation is called a flicker. The flicker can be reduced by controlling the electronic shutter to a shutter speed of n/100 seconds (n is a natural number) for a 50-Hz flicker and n/120 s for a 60-Hz flicker. To obtain the shutter speed capable of reducing the flicker so as to reduce the flicker, it is necessary to obtain the frequency of the flicker. For example, Japanese Patent Laid-Open No. 2007-60585 discloses a method of integrating video signals obtained from a CMOS sensor for one or more horizontal periods and comparing the integration values of preceding and succeeding frames to detect a flicker.
Some image capture apparatuses, which have an image sensor capable of reading out a specific region, have a function of reading out a region smaller than the entire region of the image sensor, thereby performing zooming or zooming in (i.e. magnifying) without using a zoom lens. For example, Japanese Patent Laid-Open No. 2002-314868 discloses a method of performing high-resolution zooming by changing the readout range and driving method of the image sensor.
The problem of flicker also arises when zooming is performed in this way, namely by reading out a specific region that is a sub-region of the maximum input object image receivable by the image sensor. However, the flicker can be detected using the above-described method of comparing the integration values of preceding and succeeding frames.
The prior art disclosed in the patent references above assume that the composition of the image being recorded does not change during flicker detection. If the composition does change significantly, flicker detection may be impossible. In particular, upon zooming in by reading out a specific (sub-)region, the composition often changes because of the influence of a camera shake, and accurate flicker detection may be impossible.